Fix to custom scale animations.

These now do something reasonable when performing transitions
across two activities that are both on top of the wallpaper.

Fixed computation of the pivot point of the animations.

Fixed issue where the recents panel was considered a status
bar element for purposes of deciding if the animating elements
are obscured by the status bar, which would result in us not
running the animation correctly.

Change-Id: I4b9b588b80243463e6f087a9703ee886ee281630